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THE  EFFECTS  OF  ALKALI 
ON  CITRUS  TREES 

BY 

W.  P.  KELLEY  AND  E.  E.  THOMAS 


BULLETIN  No.  318 

January,  1920 


DIVISION  OF  SUBTROPICAL  HORTICULTURE 

COLLEGE  OF  AGRICULTURE 

BERKELEY.  CALIFORNIA 


UNIVERSITY   OF  CALIFORNIA   PRESS 

BERKELEY 

1020 


EXPERIMENT  STATION  STAFF 

HEADS  OP  DIVISIONS 

David  P.  Barrows,  JMi.l).,  LL.D.,  President  of  the  University. 

Thomas  Forsyth  Hunt,  Deau, 

Kdward  J.  WiCKSON,  Horticulture  (Emeritus). 

Walter  Mulkord,  Forestry,  Director  of  Resident  Instruction. 

Herbert  J.  Webber,  Director  Agricultural  Experiment  Station. 

B.  H.  Ckocheron,  Director  of  Agricultural  Extensioru 
Hubert  E.  Van  Norman,  Vice-Director;  Dairy  Management. 

James  T.  Barrett,  Acting  Director  of  Citrus  Experiment  Station;  Plant  Path- 
ology. 
William  A.  Setchell,  Botany. 
Myer  E.  Jaffa,  Nutrition. 
Charles  W.  Woodworth,  Entomology. 
Ralph  E.  Smith,  Plant  Pathology. 
J.  Eliot  Coit,  Citriculture. 
John  W.  Gilmore,  Agronomy. 
Charles  F.  Shaw,  Soil  Technology. 

John  W.  Gregg,  Landscape  Gardening  and  Floriculture. 
Frederic  T.  Bioletti,  Viticulture  and  Enology. 
Warren  T.  Clarke,  Agricultural  Extension. 
John  S.  Burd,  Agricultural  Chemistry. 
Charles  B.  Lipman,  Soil  Chemistry  and  Bacteriology. 
Clarence  M.  Haring,  Veterinary  Science  and  Bacteriology. 
Ernest  B.  Babcock,  Genetics. 
Gordon  H.  True,  Animal  Husbandry. 
Fritz  W.  Woll,  Animal  Nutrition. 
W.  P.  Kellby,  Agricultural  Chemistry. 
H.  J.  Quayle,  Entomology. 
Elwood  Mead,  Rural  Institutions. 
H.  S.  Reed,  Plant  Physiology. 
L.  B.  Batchelor,  Orchard  Management. 
J.  0.  WiiiTTEN,  Pomology. 
Frank  Adams,  Irrigation  Investigations. 

C.  L.  Roadhouse,  Dairy  Industry. 

P.  L.  Griffin,   Agricultural  Education. 
John  E.  Dougherty,  Ptjultry  Husbandry. 
S.  S.  Rogers,  Olericulture. 
L.  J.  Fletcher,  Agricultural  Engineering. 
Edwin  C.  Voorhies,  Assistant  to  the  Dean. 

CITRUS  EXPERIMENT  STATION 

Division  ok  A(iKicuLTURAL  Chemistry 

W.  P.  Keli.f.v  *A.  B.  Cummins 

E.  H  Thomas  S.  M.  Brcavn 


*  ResiyiUMl  .June   1,   191>». 


SB 


THE  EFFECTS  OF  ALKALI  ON  CITRUS  TREES* 

By  W.  p.  KELLEY  and  E.  E.  THOMAS 


INTRODUCTION 

It  is  generally  believed  that  citrus  trees  are  especially  sensitive  to 
alkali.  One  of  the  best  known  investigations  on  the  effect  of  alkali  on 
citrus  was  published  by  Loughridge  in  1898.^  In  this  paper  it  was 
pointed  out  that  orange  trees  may  be  severely  injured  by  the  use  of 
saline  irrigation  water.  From  studies  on  certain  groves  near  Corona, 
California,  it  was  found  that  severe  injury  had  been  produced  as  a 
result  of  irrigating  with  saline  water  from  Lake  Elsinore  for  a  period 
of  from  three  to  four  years. 

Analysis  of  the  water  showed  it  to  contain  917  parts  per  million 
sodium  chloride  (common  salt),  377  parts  per  million  sodium  sulfate 
(glauber.salt),  and  391  parts  per  million  sodium  carbonate  (black 
alkali).  Loughridge  concluded  that  the  injury  to  the  trees  was  due 
directly  to  the  corrosive  action  and  puddling  effect  of  the  black  alkali 
and  indirectly  to  the  antiseptic  action  of  tlie  sodium  chloride  on  the 
bacterial  processes  of  the  soil. 

The  effects  were  more  pronounced  in  certain  groves  than  in  others. 
Inherent  differences  in  the  soil  apparently  exerted  an  influence  on  the 
depth  to  which  the  water  penetrated  and,  therefore,  caused  the  salts 
to  accumulate  in  greater  (quantities  in  the  upper  layers  of  the  soil  of 
certain  groves  than  of  others.  On  the  whole,  the  effects  were  roughly 
proportional  to  the  concentration  of  the  alkali  salts  that  had  accumu- 
lated in  the  zone  occupied  by  the  roots  of  tlie  trees. 

The  results  of  this  investigation  indicated  that  citrus  trees  are 
quite  sensitive  to  alkali,  and  tluit  the  length  of  time  a  given  supply 
of  saline  irrigation  water  may  be  used  without  producing  injury 
depends  mainly  on  the  rate  the  injurious  constituents  accumulate  in 
the  layei's  of  soil  occupied  by  the  roots  of  the  trees. 

In  1900  Ililgard-  pointed  out  that  citrus  trees  are  especially  sensi- 
tive to  sodium  chloride.     He  called  attention  to  the  previous  work  at 

*  Paper  No.  53,  University  of  California,  (iraduato  Scliool  of  Tropical  Ai;ricul- 
ture  and  Citrus  Experiment  Station.  Kiverside,  Calif. 

1  Effect  of  Alkali  on  Citrus  Trees.  Annual  IJeport,  Calif.  A<ir.  Exp.  Sta. 
1897-8,  pp.  99-113. 

2  Nature.  Value  and  Utilization  of  Alkali  Lands.  Calif.  Act.  Exp.  Sta.  Bull. 
128   (1900j.  p.   28. 

209908 


306  TNIVERSITY    OF    CALIFORNIA — EXPERIMENT   STATION 

Corona  in  wliich  it  liad  boon  found  that  2520  pounds  per  acre  of 
sodium  chloride  distributed  throuj;h  the  soil  to  a  depth  of  four  foot, 
caused  an  orange  tree  to  become  completeh'  leafless,  while  another 
tree  nearby,  wiiere  the  soil  was  similar  in  other  respects,  but  contained 
only  720  ])ounds  ]K'r  acre  of  sodium  chloride,  was  much  less  severely 
injured.  "Here  it  is  apparently  the  excess  of  common  salt  to  which 
the  difference  is  duo." 

In  1901  LougluMdge''  culled  attention  to  the  extreme  sensitiveness 
of  the  lemon  ti'oe.  He  said:  "Tlie  lemon  seems  to  be  the  least  tolerant 
of  all  of  the  fruit  trees,  for  it  was  stunted  by  1440  pounds  common 
salt  per  acre,  distributed  througli  four  feet  depth,  and  was  killed 
by  1900  pounds  combined  with  1900  pounds  carbonate  of  soda." 

In  harmony  with  the  conclusions  of  Loughridge  and  Hilgard, 
recent  investigations  by  the  writers  have  shown  that  different  varieties 
and  species  of  citrus  trees  are  quite  sensitive  to  alkali,  especially  so 
in  the  case  of  the  lemon,  and  that  after  a  few  years  irrigation  with 
saline  water,  botli  lemon  and  orange  trees  may  be  severely  injured. 
Again,  it  has  been  found  that  the  effects  produced  by  a  given  supply 
of  impure  irrigation  water  may,  for  a  time  at  least,  be  extremely 
variable  even  in  different  portions  of  the  same  grove.  Part  of  this 
variability,  as  shown  below,  is  probably  due  to  differences  in  the 
depth  to  which  the  water  penetrates,  which  in  turn  affects  the  rate  at 
whicli  the  salts  accumulate  in  the  root  zone. 

Experienee  in  various  localities  has  shown  that,  under  certain 
conditions,  continued  irrigation  with  comparatively  pure  water  also 
tends  to  hasten  tlu'  accumulation  of  injurious  amounts  of  soluble  salts. 
Several  hundred  tliousaiid  acres  located  in  different  parts  of  Califor- 
nia, whicli  were  free  from  injurious  amounts  of  alkali  previous  to  the 
introduction  of  irrigation,  have  since  become  veritable  alkali  lands. 
Seepage,  togctlicr  with  a  rising  water  table  incident  to  over-irrigation, 
have  been  the  ])rineipal  means  by  whicli  tlie  salts  have  been  brought 
u]i  from  below  and  deposited  near  the  surface.  Small  areas  of  citrus 
gi-oves  liave  ali'eady  become  heavily  charged  witli  alkali  by  this  means. 

In  the  course  of  investigations  on  the  nutrition  of  citrus  trees,  we 
have  dt'voted  considerable  study  to  certain  phases  of  the  alkali  prob- 
lem. Early  in  this  work,  it  became  evident  that  the  existing  state  of 
knowledge  was  inade(iuate.  The  symptoms  of  alkali  injury  have  not 
l)een  recognized  clearly.  The  relations  of  fertilizers  to  the  problem, 
and  esjiecially  the  elfet-t  of  ajiplying  irrigation  water  containing  alkali 
salts,  are  inadecjuately  understood  and  appreciatid. 


3  Tolerance   of  Alkali  l)v   Various   Cultures.      Calif.   A-^r.    Exp.    Sta.    Bull.    133 
(1901),  pp.  14-1(>. 


Bulletin   318         the    effects    OF    ALKALI    ON    CITRUS    TREES  307 

It  is  commonly  held  that  alkali  injury  is  mainly,  if  not  entirely, 
due  to  excessive  concentration  as  such.  In  the  course  of  this  work, 
it  has  become  evident,  however,  that  injury  may  be  produced  under 
certain  conditions  where  the  total  concentration  is  relatively  low. 
The  data  obtained  in  a  study  of  this  phase  of  the  subject  afford  the 
basis  for  an  interesting  hypothesis  whicli  will  be  presented  elsewhere 
and  further  work  is  in  progress.  The  discussion  in  this  bulletin  will 
be  confined  mainly  to  the  effects  of  exc(  ssive  concentration. 

As  this  work  has  progn  ssed,  it  has  become  increasingly  evident 
that  many  of  the  citrus  growers  of  California  have  not  sufficiently 
grasped  the  significance  of  alkali  in  citrus  culture.  Especially  is  this 
true  in  regard  to  the  bearings  of  impure  irrigation  water  on  the 
accumulation  of  alkali  in  the  soil.  Fortunately,  a  large  percentage 
of  the  citrus  soils  was  free  from  alkali  previous  to  the  introduction  of 
irrigation  and  very  much  of  it  still  remains  free.  There  are  con- 
siderable areas  located  in  several  districts,  however,  where  harmful 
amounts  of  alkali  have  accumulated  as  a  result  of  applying  saline 
irrigation  water  and  still  other  areas,  not  yet  seriously  injured,  where 
alkali  is  accumulating  at  present  as  a  result  of  orchard  practices  which, 
if  continued,  will  ultimately  produci'  injury. 

This  bulletin  will  be  devoted  to  a  discussion  of  results  obtained  in 
connection  with  a  study  of  a  considerable  number  of  citrus  groves  in 
different  localities  in  California.  The  investigations  reported  herein 
deal  mainly  with  the  effects  of  alkali  rather  than  with  means  of  over- 
coming the  injury.  It  is  undoubtedly  a  matter  of  practical  importance 
for  citrus  growere  to  be  able  to  recognize  the  effects  of  alkali  and 
especially  to  appreciate  the  relationsliips  between  existing  orchard 
practices  and  the  accumulation  of  alkali. 

Unfortunately,  the  present  state  of  knowledge  does  not  yet  make 
it  possible  to  predict  with  as  great  a  degree  of  certainty  as  is  desirable, 
what  the  effects  of  a  given  amount  of  alkali  will  be,  or  how  long  a  given 
saline  irrigation  water  may  be  apj)lied  before  producing  injury.  The 
extreme  variability  of  soils  and  the  inade(iuaey  of  knowledge  concern- 
ing the  fundamental  relationships  between  salts  and  soils,  and  salts 
and  plant  growth,  add  to  the  difficulty.  Desi)ite  these  facts,  informa- 
tion of  some  practical  im])ortanee  has  been  obtained. 

The  investigations  reported  herein  should  be  looked  upon  as  being 
preliminary  to  a  study  of  methods  of  eonibatiiig  alkali  in  citrus 
groves.  It  is  hoped  that  this  discussion  will  enable  citi-us  growei-s  to 
recognize  the  effects  of  alkali,  to  apjin  ciatc  Ihc  sci-imisness  of  alkali 
m  citrus  culture,  to  apprelieiid  mow  cleai'ly  1h(>  relationships  between 
irrigation  and  the  aceunuilatioii  of  alkali,  and  to  sec  that  the  aiii)liea- 

UiVlh^l'N  Ot-   SUblHuI'lCAL  HORTlCULTUKt 
'  OP  AGRICUl"   ^ 


308  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION 

tion  of  certain  fertilizers,  especially  nitrate  of  soda,  may,  under  certain 
conditions  at  least,  bear  a  very  important  relation  to  the  accumulation 
of  alkali.  Witli  this  knowledfje,  it  is  hoped  that  practical  citrus 
growers  will  be  able  to  adjust  their  irrigation  and  fertilizer  practices 
in  such  a  way  as  to  retard  the  further  spread  of  alkali  and  thus 
prevent  its  accumulation  in  many  groves  that  have,  as  yet,  not  been 
seriously  injured. 

SYMPTOMS   OF  ALKALI    INJURY 

DiflPerent  varieties  and  species  of  citrus  trees  are  affected  differently 
by  alkali.  Lemon  trees  show  the  effects  by  a  pronounced  yellowing 
of  the  margins  and  burning  of  the  tips  of  the  leaves,  followed  by 
unusually  heavy  shedding  of  the  leaves  in  the  latter  part  of  the  winter 
and  spring.  The  subsequent  new  growth  may  appear  to  be  quite 
normal  and  vigorous  for  several  mouths,  but  later  a  large  portion  of 
the  leaves  turn  yellow  in  irregularly  sliaped  areas  around  the  margins 
and  fall  excessively.  In  the  presence  of  excessive  concentrations  of 
salts,  especially  chlorides,  complete  defoliation  may  take  place.  Mottle 
leaf  frequenth'  occurs,  and  sometimes  chlorosis.  Both  the  quality  and 
quantity  of  the  fruit  are  impaired. 

Orange  trees  also  show  the  effects  of  alkali  in  different  ways.  On 
certain  soils,  mottle  leaf  is  one  of  the  first  symptoms.  In  some  locali- 
ties, the  older  leaves  assume  a  brownish  hue  and  tend  to  curl  slightly. 
Rather  sudden  defoliation  takes  place,  especially  when  excessive 
amounts  of  chloride  occur,  followed  later  by  a  profuse  growth  of  new 
shoots.  The  leaves  of  the  new  growth  are  likely  to  be  undersized  and 
paler  in  color  than  normally.  With  especially  high  concentrations  of 
sulfates  and  bicarbonatcs  in  the  soil,  orange  leaves  become  chlorotic 
and  strikingly  similar  to  that  condition  referred  to  by  Hilgard*  as 
occurring  on  highly  basic  soils.  The  smaller  twigs  may  be  killed. 
Frequently  the  leaves  are  abnormally  small  on  one  portion  of  a  tree, 
and  full-sized  on  others. 

Premature  shedding  of  the  leaves  takes  place  with  both  oranges 
and  lemons  affected  by  small  amounts  of  alkali,  which  may  be  pro- 
tracted throughout  tlie  greater  part  of  the  winter  mouths,  thus  greatly 
reducing  the  number  of  leaves  remaining  on  tlie  trees  at  the  close  of 
the  dormant  ])eriod.  Navel  oranges  are  more  sensitive  than  Yalencias, 
and  Eureka  lemons  more  sensitive  than  Lisbons.  In  general,  lemon 
trees  are  more  sensitive  than  orange  trees.     Neither  orange  nor  lemon 


■1  Marlv  subsoils  and  tlic  Clilurosis  or  Yellowing  of  Citrus  Trees.     Calif.  A^. 
Exp.  Sta.'Cir.  Xo.  27  (lOOC). 


Bulletin  318       the  effects  OP  aekaei  on  citri's  trees  309 

trees  reach  their  usual  size  on  soil  that  contains  injurious  amounts  of 
alkali. 

It  has  been  found  that  oran«:e  trees  affected  by  alkali  are  unusually 
susceptible  to  injury  from  adverse  climatic  conditions.  Hot  winds 
burn  the-  young  leaves  and  frosts  produce  more  serious  injury  than 
with  normal  trees.  Alkali  injury  is  also  accentuated  by  the  lack  of 
care,  such  as  improper  tillage,  the  insufficient  use  of  manure  or  other 
fertilizer,  and  withholding  irrigation,  tlicrcby  allowing  the  soil 
to  become  too  dr3\  If  the  soil  by  allowed  to  dry  out  excessively,  the 
concentration  of  alkali  in  the  soil  moisture  may  become  harmful, 
while  a  more  abundant  supply  of  water  would  so  dilute  the  salts 
present  as  to  reduce  the  concentration  to  a  point  where  normal  growth 
could  take  place. 

THE    EFFECTS    OF   IRRIGATION    WATER 

Despite  the  wide  publicity  that  has  been  given  the  subject  of 
irrigation  waters  and  the  many  analyses  that  were  published  by 
Plilgard  in  the  reports  of  the  California  Station,  our  studies  in  the 
different  citrus  districts  suggest(  d  the  desirability  of  making  a  survey 
of  the  irrigation  water  in  use  at  present.  oMore  than  a  thousand 
samples  have  been  analyzed.  It  has  been  found  that  the  vast  majority 
are  practically  free  from  alkali.  Especially  is  this  true  of  the  water 
that  is  drawn  from  points  located  near  the  large  watersheds,  such,  for 
example,  as  the  Sierra  Nevada  and  the  San  Bernardino  mountains. 
Usually  the  wells  that  are  located  near  tlie  course  of  streams  that 
originate  in  those  mountains  are  also  sufficiently  pure. 

On  the  other  hand,  wells  located  at  some  distance  from  the  large 
watersheds  and  relatively  large  streams  that  tliemselves  originate 
directly  in  the  mountains,  show  a  wide  range  in  eomposilion.  A  con- 
sideral)le  iuiml)er  of  such  wells  contain  notable  amounts  of  salts. 
These  are  widely  distributed  over  a  considerable  number  of  citrus  dis- 
tricts in  several  counties.  Tn  certain  localities  the  dissolved  salts  are 
predominantly  chlorides,  others  sulfates  and  in  still  others  biearbon- 
ates.  A  few  wells  have  been  found  to  eontaiji  large  amounts  of 
nitrates. 

The  results  of  this  survey  ai-e,  on  tlie  whole,  in  elose  agreement 
with  the  ])ul)lished  conclusion  of  Dr.  llilgard.  We  (piote  from  him 
as  follows:'"' 

"The  investigations  made  by  tlie  Station  have  sliown  that  aside 
fnmi  the  freipiently  saline  cluiivieter  of  the  well  and  even  the  artesian 

M'alif.  Agr.  Exp.  Sta.  Iliill.   128    (IDOO),  p.  :il. 


310  UNIVERSITY    OP    CALIFORNIA — EXPERIMENT   STATION 

waters  of  the  iictrolciim  bearino:  regions  of  the  State  in  tlie  coast 
ranges,  the  streams  of  that  region,  especially  the  smaller  ones,  are 
sometimes  too  strongly  charged  with  alkali  (in  this  case  largely  the 
snlfates  of  soda  and  magnesia)  to  be  snitable  either  for  irrigation 
or  domestic  nse.  Towards  the  end  of  the  dry  season,  even  the  larger 
streams  of  the  southern  coast  ranges,  with  their  diminished  flow,  some- 
times show  an  excess  of  salts.  Tliis  seems  also  to  be  true  of  the  San 
Jacinto  river,  which  feeds  Elsinore  Lake."  On  the  other  hand,  he 
says:  ''The  wati'rs  flowing  from  the  Sierra  iNIadrc,  south  of  the 
Tehachapi  range,  are  tliroughout  of  excellent  ([uality  for  irrigation 
purpos(>s,  as  are  all  those  flowing  from  the  Si(>rra  Nevada.  The  same 
is  true  of  the  artesian  waters  of  the  valley  of  southern  California,  from 
Los  Angeles  east  to  Redlands." 

A  considerable  number  of  groves  that  have  been  irrigated  with 
saline  water  have  been  under  close  observation  for  one  or  more  years. 
As  a  means  of  securing  information  on  the  effects,  soil  samples,  drawn 
with  a  one-inch  soil  tube,  have  been  analyzed  and  wherever  possible 
adjacent  areas  that  have  been  irrigated  with  comparatively  pure 
water,  or  virgin  soil,  have  also  been  sampled.  Some  of  the  results  are 
submitted  below,  together  with  analyses  of  the  irrigation  waters  that 
have  been  applied. 

The  analytical  results  are  expressed  as  parts  per  million  of  the 
soil  or  water.  In  contrast  to  previous  publications,  we  have  not 
attempted  to  estimate  the  amounts  of  the  several  salts  present.  The 
state  of  present  knowledge  does  not  make  it  possible  to  determine 
definitely  the  actual  amounts  of  the  different  salts  that  occur  in  com- 
plex mixtures,  such  as  irrigation  waters  or  soils.  By  analysis  the 
components  of  the  different  salts  may  be  determined,  but  while  vari- 
ous schemes  have  lieen  employed  for  calculating  the  amounts  of  salts 
present,  all  of  them  are  more  or  less  arbitrary  and  have  little  justi- 
fication in  modern  cliemistry.  Accordingly,  the  analytical  data  are 
submitted  as  determined  without  calculating  the  theoretical  salt  com- 
binations. 

The  analyses  recorded  in  table  1  have  been  chosen  to  show  the 
wide  range  in  e()m]iosition  found  among  tlie  irrigation  supplies.  Some 
of  these  contain  large  aniounls  of  salts,  othei's  lesser  amounts.  As 
will  1)('  ]ioiiit('d  out  more  fully  below,  the  effi'cts  of  some  of  these 
waters  liave  been  extremely  injurious.  Sample  No.  84  represents  suit- 
able water.  This  sam])le,  drawn  from  wells  loeat(  d  near  the  San 
Bernardino  ^Mountains,  fairly  represents  the  main  supplies  of  moun- 
tain water  of  southern  California,  the  effects  of  which  have  been 
entirelv  satisfactorv. 


Bulletin  318        r|,jjj^   EFFECTS   OF   ALKALI   OX    CITKIS   TREES  311 

It  is  not  necessary  to  discuss  the  amounts  of,  and  variations  among, 
the  individual  constituents  of  these  waters.  Casual  observation  of 
tlie  analyses  will  suffice  to  show  tiuit  there  is  a  v/ide  range  of  difference 
in  the  content  of  total  dissolved  materials  and  that  a  number  of  the 
individual  constituents  occur  in  certain  samples  in  relatively  large 
amounts.  The  most  significant  differences  in  these  watei's  probably 
lie  in  the  chlorine  and  sodium.  The  unusually  high  nitrate  content 
of  sample  No.  119  is  a  matter  of  special  interest.  Where  such  water 
is  used  for  irrigation,  it  is  highly  improbable  that  nitrogenous  ferti- 
lizers will  be  needed. 

The  variations  f(mnd  among  sami)les  that  contain  relatively  large 
amounts  of  salts,  such,  for  example,  as  Nos.  C42  and  643,  are  probably 
of  little  practical  significance.  On  the  other  hand,  samples  Nos.  103 
and  105  contain  still  greater  amounts  of  salts,  especially  so  in  the 
case  of  the  latter.  Sample  No.  150  is  of  intermediate  composition  and 
represents  a  type  of  water  that  is  being  used  at  present  on  several 
thousand  acres  of  citrus  in  California.  As  will  be  pointed  out  later, 
the  use  of  this  water  on  a  lemon  grove  for  a  period  of  approximately 
twenty  years,  produced  definite  injury. 

The  numbers  of  pounds  of  a  given  constituent  that  will  be  added 
to  the  soil  by  an  irrigation  water  may  be  readily  calculated  from  the 
analysis.  For  example :  an  acre  foot  of  water,  No.  119,  which  contains 
1479  parts  per  million  soluble  solids,  will  supply  the  soil  3993  pounds 
of  solids,  while  an  acre  foot  of  No.  84,  containing  222  parts  per  million, 
will  add  only  599  pounds.  In  view  of  the  fact  that  the  amounts  of 
water  ap])lied  varies  widely  in  different  localities  and  in  different 
years  in  a  given  grove,  it  is  not  ]K)ssible  to  state  the  exact  amounts 
of  salts  that  have  been  added  to  the  soil  in  a  given  case.  It  is  only 
possible  at  present  to  make  qualitative  comparisons  among  the  groves. 
It  is  evident,  however,  that  large  amounts  of  alkali  nuist  necessarily 
have  been  adth  d  to  the  soil  where  such  water  as  Nos.  119,  642  and  643 
have  been  applied.  Still  greater  amounts  nnist  have  been  added  in 
a  given  period  witli  Nos.  103  and  105,  while  with  No.  150,  tlie  rate  of 
salt  addition  has  been  considerably  less. 

During  the  past  eight  years,  several  hundred  acres  of  orange 
orchards  located  near  Riverside,  which  were  previously  irrigated  with 
suitable  water,  have  be<']i  irrigated  with  saline  water  similar  to  samples 
Nos.  119,  642  and  643.  Other  groves  adjacent  1o  these  have  been 
irrigated  from  the  beginning  with  eouiparatively  pure  water  (No. 
84).  So  far  as  can  now  be  detei'inined,  the  soil  in  this  innnediate 
locality  was  i'easona])ly  unii'oi'm  and  i'vvv  from  alkali  previous  to 
planting  the  orcliai'ds.     Tlie  soil  is  of  a  sandy  loam  cliaractei',  reason- 


312  UNIVERSITY    OP    CALIFORNIA — EXPERIMENT    STATION 

ably  deep  and  free  from  hardpaii.  Throughout  this  district,  the 
soil  is  deficient  in  organic  matter  and  nitrogen,  the  liberal  application 
of  both  of  which  is  required  for  successful  citrus  culture. 

The  orange  trees  are  about  twenty-four  years  old.  A  number  of 
these  groves  have  been  under  close  observation  for  a  period  of  about 
three  years.  A  large  portion  of  the  trees  irrigated  with  the  saline 
water  have  already  been  severely  injured ;  some  of  them  are  almost 
dead  and  a  large  portion  unprofitable.  The  degree  of  the  injury  is 
much  more  pronounced  at  the  present  time  (1919)  than  it  was  in  1917, 
while  in  1916  injurious  effects  had  scarcely  begun  to  appear.  The 
•accompanying  photographs,  plates  1  and  2,  illustrate  the  effects  and 
show  the  appearance  of  the  trees  in  the  spring  of  1919.  They  show 
the  striking  contrast  between  the  effects  of  good  irrigation  water  and 
water  containing  alkali  salts.  In  portions  of  the  groves  where  the 
saline  water  has  been  applied,  excessive  defoliation  has  taken  place 
several  times.  ]\Iany  of  the  smaller  branches  have  died  and  the  new 
foliage  has  shown  excessive  mottle  leaf. 

Soil  samples  from  a  number  of  these  groves  have  been  analyzed. 
Some  of  the  results  are  submitted  in  tables  2,  3,  4,  5  and  6.  The  data 
show  that  the  total  soluble  salt  content  of  the  soil  and  the  amounts  of 
certain  individual  constituents  have  been  greatlj^  increased  as  a  result 
of  irrigating  with  saline  water.  The  chlorine  and  sodium  content  have 
been  increased  to  the  greatest  extent.  Other  constituents  have  also 
been  augmented  considerably. 

The  data  show  a  direct  relationship  between  the  salt  content  of  the 
soil  and  the  composition  of  the  irrigation  water,  and  the  condition  of 
the  orange  trees  is  positively  correlated  with  the  salt  content.  It  is 
evident,  however,  that  orange  trees  are  extremely  sensitive.  The  total 
concentration  of  soluble  matter  in  a  number  of  the  samples  was  not 
more  than  0.10  per  cent  (1000  parts  per  million),  even  where  the  trees 
have  been  severely  injured.  The  soil  samples  represent  composite 
mixtures  of  a  considera])le  number  of  cores,  taken  at  random  from  the 
spaces  between  tlie  trees  where  the  irrigation  waters  have  been  applied. 
Under  the  prevailing  system  of  furrow  irrigation  soluble  salts  tend  to 
accumulate  in  greatest  amounts  between  the  irrigation  furrows  and  in 
the  unirrigated  spaces  between  the  trees,  owing  to  lateral  movement. 
Consequently,  higher  concentrations  ])robably  occur  in  localized  areas 
between  the  furrows,  tlian  were  found  in  the  samples  analyzed.  Wliile 
orange  trees  are  more  sensitive  to  alkali  tlian  many  other  crops,  it  is 
reasonably  certain  tliat  with  tlie  coiitiiuied  use  of  these  waters  the 
soil  will  become  so  heavily  charged  with  alkali  as  to  impair  its  useful- 
ness for  the  more  resistant  crops. 


Bulletin  318        the   EFFECTS   OF   alkali   on   CITRl'S   TREES 


313 


The  data  in  tables  4,  5  and  6  show  that  the  salts  have  evidently 
penetrated  to  considerable  depths.  Samples  were  taken  in  three  groves 
to  a  depth  of  seven  feet,  two  of  which  have  been  irrigated  with  saline 
water  (No.  643),  the  other  witli  comparatively  pure  water  (No.  84). 


Fig.  1. — Orange  trees  irrigateil   witli  saline  water,  Xo.  ()4." 


Fig.     2.— C;...M^,       1,^>-^     i.r.^aK.i      ,\it:,     ;4,..,.      v>„M,.      :x,..     >>-f. 

Tlie  analyses  estal)lisli  the  fact  tliat  the  salts  have  penetrated  deejily. 
The  data  su<i'<i'('st  that  the  jx'iicti'ation  has  even  reaelied  det'i^er  than 
s(>V(Mi  feet,  but  sniiiples  have  not  been  di'awn  fi'oni  ui'cater  dei^ths. 

The  analyses  of  samples  from  the  (lifrcreiit  ^n-oves  that  have  been 
irri^-a1(>d  with  pure  water  indicate  that  the  oriu-iiuil  soil  must  have 
varied  considerably.    The  variations  are  not  surprising',  liowever,  since 


314  UNIVERSITY    OF    CALIKORNIA — EXPERIMENT    STATION 

the  difforoiit  groves  from  which  these  samples  were  taken  are  located 
considerable  distances  apart.  It  may  be  mentioned  in  passing,  tliat 
more  or  less  mottle  leaf  occnrs  in  many  of  the  groves  in  this  locality 
that  have  been  irrigated  with  comparatively  pure  water.  In  such 
cases,  the  cause  of  the  mottle  leaf  inheres  in  the  soil  itself.  Consider- 
ably more  mottle  leaf  occurs  in  grove  E  than  in  groves  M  or  S.  It 
is  interesting  to  note  that  the  soil  of  the  former  differs  considerably 
from  that  of  the  two  latter.  Further  discussion  on  tliis  point  will  bo 
submitted  elsewhere. 

In  addition,  tlie  vertical  distribution  of  salts  varies  in  different 
groves  under  the  same  saline  irrigation  supply.  (Compare  the  data 
from  groves  0  and  C,  tables  4  and  6.)  It  is  not  possible  at  present  to 
explain  these  variations.  Differences  in  the  amounts  of  water  applied, 
in  cultural  operations  and  in  tlie  degree  of  compactness  of  the  subsoil, 
are  probably  among  the  most  imjiortant  factors. 

While  large  portions  of  tlusc  groves  have  been  severely  injured, 
it  is  interesting  to  note  that  tiie  effects  have  not  been  uniform  over 
the  entire  area  that  has  been  irrigated  with  saline  water.  In  some 
places,  little  or  no  effects  were  evident  in  1918,  and  again  in  1919 
the  degree  of  injuiy  was  still  much  h  ss  pronounced  in  certain  places 
than  in  others.  It  is  important,  however,  that  some  of  the  trees  which 
were  healthy  in  1917  have  since  begun  to  show"  definite  signs  of  injury. 
Soil  samples  have  been  drawn  from  among  the  severely  injured  trees  of 
the  grove  (B)  and  from  an  area  of  the  same  grove  where  the  trees 
have  been  only  slightly  injured.  Analyses  of  these  samples  are 
submitted  in  table  7. 

The  results  show  that  the  subsoil  below  the  second  foot  of  the 
severel}'  injured  area  contains  considerably  more  salts  than  in  the  less 
injured  portion.  Especially  is  this  true  of  the  chlorine  and  sodium, 
the  two  constituents  that  seem  to  be  most  responsible  for  the  injury 
in  these  groves.  These  variations  are  probably  due  to  inherent  differ- 
ences in  the  physical  nature  of  the  subsoil  which  are  such  as  to  modify 
the  rates  of  ])enetration  and  accumulation  of  salts.  At  any  rate,  it  is 
interesting  that  the  more  severe  injury  has  taken  place  where  the 
greater  amounts  of  salts  liave  accumulated.  As  already  pointed  out, 
the  least  affected  jiortions  of  this  gi-ove  have  now  begun  to  show  definite 
injui'y.  It  is  liighly  probable  that  the  injury  will  become  severe  over 
tlu^  entiri*  orchai'd  if  tlie  use  of  the  ])resent  irrigation  supply  be  not 
discontinued.  ''         >  iil 

As  bearing  further  on  the  variability  of  the  effects  of  saline  irriga- 
tion water,  studies  have  been  nuule  on  the  chemical  reactions  that  take 
place  when  salts  are  added  to  soils.     It  has  been  found  that  alkali  salts 


Bulletin  318       the  effects  OF  alkali  ox  citrcs  trees  315 

have  the  power  of  reacting  witli  lieavy  tyi)es  of  soils  to  a  greater  degree 
than  with  sandy  soils.  The  reactions  result  in  removing  limited 
amounts  of  sodium  from  solution  and  bringing  into  solution  corre- 
sponding amounts  of  other  bases,  composed  mainly  of  calcium.  The 
physical  arrangement  of  the  soil  particles  also  undergoes  alteration. 
In  view  of  the  fact  that  soils  are  extremely  variable,  it  is  not  surpris- 
ing, that  the  efi'ects  of  irrigation  have  not  been  uniform  over  a  given 
grove. 

Analyses  of  two  irrigation  waters  from  Tulare  County  are  also 
reported  in  table  1  (Nos.  103  and  105).  They  contain  unusually 
large  amounts  of  salts.  Information  at  hand  does  not  made  it  possible 
to  state  the  exact  length  of  time  these  waters  have  been  applied.  The 
wells  from  which  the  samples  were  drawn  were  deepened  about  four 
years  previously  and  there  is  some  evidence  that  water  of  a  radically 
different  character  was  obtained  as  compared  with  that  originally 
supplied.  It  is  probable  that  one  of  these  wells  (No.  103)  supplied 
fairly  pure  water  previous  to  being  deepened.  The  orange  trees  to 
which  these  waters  have  been  applied  are  approximately  twelve  years 
old  and  have  shown  severe  injury  during  the  past  two  years. 

Soil  samples  were  drawn  from  these  groves  and  also  from  adjacent 
unirrigated  fields  apparently  similar  in  every  way  to  the  soils  in  the 
groves.  One  of  these  has  been  used  for  grain  for  a  number  of  years, 
the  other  still  remains  in  its  native  state.  The  soil  of  one  of  these 
groves  (T)  is  of  a  sandy  loam  character  most  of  which  is  underlaid 
with  a  dejLse  hardpan  at  a  depth  of  from  two  to  three  feet.  The  other 
is  located  on  the  heavy  type  of  soil,  belonging  to  the  Porterville  clay 
loam  adobe  series,  locally  knowii  as  "dry  bog."  The  analyses  are 
reported  in  tables  8  and  9. 

The  data  confirm  the  results  obtained  in  tlie  study  of  the  groves 
located  near  Kivcrside.  By  comparing  the  irrigated  witli  the  unirri- 
gated soils,  it  is  seen  at  once  that  the  irrigation  has  greatly  increased 
the  amounts  of  soluble  salts  in  the  soil.  While  the  concentration  of 
practically  eveiy  constituent  has  been  increased,  the  chlorine  and 
sodium  have  been  increased  to  the  greatest  extent.  Comparison  of  the 
soil  analyses  witii  those  of  the  irrigation  waters  shows  that  those  con- 
stituents jireseiit  in  tlie  water  in  greatest  amounts  have  accumulated 
in  the  soil  to  the  greatest  extent.  The  rates  of  iiierease,  Jiowever.  are 
not  proportional  to  the  eompositioii  of  tlie  irrigation  water,  owinir  in 
part,  at  least,  to  the  fact  that  citrus  ti-ees  al)sorb  large  amounts  of 
certain  constituents,  and  only  small  aiuduiits  of  otliei-s.  As  will  l)e 
shown  elsewhere,  citrus  ti'ets  do  not  absorb  sodinni  salts  to  anv  ureal 
extent,  but  absorb  relatively  large  amounts  of  calcium. 

DIVISION   Of   SUHIKliPirAl   HORIICULIUK^ 
COLLEGE  OF  AGRICULTURE 


316  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 

It  is  iiilcn'stintj  to  note  in  this  coiiucction  that  navel  orange  trees 
are  l)ein<2:  <i:r()wn  on  one  j)ortion  of  each  of  these  groves,  and  Valencia 
oranges  on  anothei-.  In  eaeii  ease,  the  navels  were  injured  in  a 
sliorter  jx'riod  of  time  than  the  Vali'neias.  In  faet,  some  of  the  Valen- 
eias  of  grove  T,  located  in  a  portion  of  the  field  where  the  soil  is  six 
or  more  feet  deep,  have  not  as  yet  been  severely  injured,  but  even  that 
l^ortion  of  the  Valencia  trees  located  on  sliallow  soil  similar  to  the 
luivel  area  have  been  less  severely  injured  than  the  navels.  In  grove 
II,  tlie  Valrfncias  were  much  less  severely  injured  in  1918  than  the 
navels.  It  is  important  to  state,  however,  that  many  of  the  Valencia 
trees  in  the  latter  grove  have  shown  seven;  injury  in  1919.  These 
facts,  together  with  observations  in  other  localities,  indicate  that 
Valencia  oranges  are  more  resistant  to  alkali  than  navel  orange  trees. 
But  it  must  not  be  concluded  tiuit  the  former  are  highly  tolerant  of 
alkali,  for  such  is  not  the  case.  The  use  of  irrigation  water  containing 
alkali  salts  will  ultimately  produce  iiijuiy  to  either  variety,  it  being 
mainly  a  matter  of  the  length  of  time. 

A  lemon  grove  located  near  San  Diego  luis  also  been  studied.  The 
trees  are  about  sixteen  years  old  and  have  been  irrigated  from  the 
time  of  planting  witli  saline  water  No.  G89.  During  the  past  two  or 
three  years,  a  portion  of  the  trees  have  shown  signs  of  injury,  many 
of  them  severely  so.  ]\Iost  of  the  older  leaves  throughout  the  grove 
have  turned  yellow  around  the  nuirgins  and  brown  at  the  tips.  A 
large  proportion  of  the  leaves  have  fallen  in  certain  places,  the  smaller 
shoots  have  di(  d  and  the  economic  value  of  some  of  the  trees  has  been 
greatl}'  impaired. 

Referring  again  to  the  table  of  water  analysis,  it  will  be  seen  that 
the  irrigation  water  (table  1,  No.  689)  contains  considerable  amounts 
of  alkali  salts,  being  composed  in  this  case  largely  of  sodium  chloride. 
Soil  sam})les  were  drawn  from  tliis  grove  to  a  depth  of  two  feet 
and  also  from  an  adjacent  unirrigated  field.  Their  analyses  are  given 
in  tal)le  10.  In  harmony  with  the  results  ah'eady  discussed,  it  is  shown 
that  the  concentration  of  salts  has  been  materially  increased  as  a 
result  of  irrigation.  Tlie  luuisually  high  soluble  potassium  content 
of  the  first  foot  of  the  irrigated  soil  is  especially  noteworthy  and  is 
probably  due  to  tlie  liberal  use  of  fertilizers  and  manure. 

The  irrigation  waters  discussed  above  contain  relatively  large 
amounts  of  salts.  Some  of  them  contain  amounts  of  alkali  salts  that 
might  reasonably  have  been  cxpeeti'd  to  produce^  injury.  Under  the 
conditions  of  soil  and  subsoil,  as  they  exist  in  these  groves,  it  would 
have  been  surprising  iiuleed  to  iind  that  injury  had  not  been  produced 
bv  these  waters.     It  is  interesting  in  this  connection  that  the  effects 


Bulletin  318       the  effects  of  alkali  on  citrus  trees  317 

produced  by  the  irrij^ation  waters  discussed  above  are  quite  similar 
to  the  effects  produced  at  Corona  by  water  from  Lake  Elsinore  more 
than  twenty  years  ago.  Tlie  analyses  reported  by  Lough  ridge  also 
show  that  the  salt  content  of  Lake  Elsinore  was  actually  less  than 
that  of  some  of  the  present  supplies.  It  would  seem  that  the  unfor- 
tunate experience  at  Corona  has  either  been  forgotten  or  largely  over- 
looked by  citrus  growers. 

In  addition  to  the  above  and  a  considerable  number  of  other  saline 
irrigation  supplies,  that  are  at  present  being  applied  to  certain  citrus 
groves  in  California,  there  is  a  much  larger  quantity  of  the  irrigation 
water  that  contains  somewhat  smaller  amounts  of  alkali  salts.  In  view 
of  the  economic  a-spects  of  this  phase  of  the  subject,  it  is  a  matter  of 
interest  to  study  the  effects  of  this  latter  class  of  waters.  For  this 
purpose,  a  lemon  grove  has  been  chosen.  While  the  irrigation  supply 
in  this  case  has  been  drawn  from  more  than  one  source,  the  proportions 
of  which  have  varied  from  time  to  time,  the  analysis  given  in  table  1 
(no.  150)  probably  represents  the  average  composition  of  the  water. 
It  contains  considerably  less  alkali  than  the  irrigation  waters  discussed 
above.  As  judged  by  current  standards,  this  water  woidd  certainly 
not  be  considered  to  be  excessively  saline. 

The  lemon  trees,  now  twenty  years  old,  grew  thriftily  and  produced 
heavy  crops  of  fruit  for  many  years.  During  the  past  two  or  three 
years,  however,  some  of  them  have  begun  to  decline.  Tiie  older  leaves 
have  turned  yellow  or  brown  and  liave  fallen  excessively  in  the  winter 
and  spring.  ]\Iany  of  the  trees  have  lost  their  former  thrift  and  the 
yields  and  quality  of  tlie  fruit  have  been  considerably  reduced,  in 
spite  of  the  fact  that  reasonably  good  care  and  liberal  amounts  of 
manure  and  other  fertilizers  have  been  applied. 

Soil  samples  have  l)een  analyzed  from  tliis  grove,  and  also  from 
an  area  near  by  that  has  been  under  irrigation  with  water  from 
the  same  source  for  only  two  years.  The  results  are  submitted  in 
table  11.  The  data  show  tliat  the  total  soluble  matter  has  been  very 
materially  increased  as  a  result  of  the  longer  period  of  irrigation. 
Considerable  amounts  of  sodium  salts,  composed  principally  of  the 
chloride,  have  accumlated  in  the  soil.  Sulfate  has  also  increased 
considerably.  It  is  again  found  that  the  greatest  increases  have 
taken  place  among  those  constituents  tliat  are  absorl.)ed  l\v  lemon  trees 
in  least  amounts  and  have,  at  tlie  same  time,  been  added  in  greatest 
amounts  in  the  irrigation  watei". 

As  might  have  been  jirt'dieted  from  the  aiuilysis  of  tlie  water,  it 
has  re(|iiire(l  a  longer  period  of  time  1o  et'feet  a  given  iiierease  in  the 
concentration  of  salts  in  this  grove  than  has  bt'i-n  rei^uired  wliere  some 

DIVISION  OF  SllbiK'iFICAl.  HORIlCULIU^f 
COLLEGE  OF  AGRICi: 


318  UNIVERSITY   OP    CALIFORNIA — EXPERIMENT    STATION 

of  tlie  more  liighly  saline  waters  have  been  applied.  The  data  show, 
however,  that  the  alkali  eontent  of  the  soil  may  ultimately  reach  a 
harmful  eoneentration  whei-e  irri<?ation  water  is  applied  that  contains 
only  a  relatively  low  eoneentration  of  alkali  salts. 

It  should  not  be  inferred  that  the  application  of  water  similar  to 
samjilc  No.  150  will  always  jiroduee  the  same  degree  of  injury;  certain 
other  lemon  groves  of  ai)i)r()xinuitely  the  same  age  have  been  irrigated 
with  the  same  supply  as  grove  (L),  which  do  not,  as  yet,  show  any 
apparent  injury.  Samples  of  soil  from  these  groves  have  not  been 
analyzed. 

Taken  in  their  entirety,  the  above  investigations  show  a  remarkably 
close  relationship  between  the  composition  of  the  irrigation  water,  on 
the  oiu'  hand,  and  the  accumulation  of  alkali  salts  and  the  condition 
of  the  orange  and  the  lemon  trees,  on  the  other.  In  every  case  we  have 
studied,  where  saline  irrigation  water  ha.s  been  applied  for  a  period 
of  years,  alkali  salts  have  accumulated  in  the  soil  and  the  citrus  trees 
have  been  injured  in  consequence.  The  rates  at  which  salts  have 
actually  accumulated  vary,  however,  in  different  soils,  depending  on 
(1)  the  composition  of  the  water,  (2)  the  amounts  applied,  and  (3) 
the  freedom  with  which  it  penetrated  into  the  subsoil. 

It  must  be  apparent  from  the  above  discussion  that,  although  the 
content  of  alkali  in  an  irrigation  water  may  not  be  directly  injurious, 
the  time  may  come  after  it  has  been  applied  for  a  period  of  years, 
when  exceedingly  harmful  amounts  of  salts  will  accumulate  as  a  result 
of  evaporation  and  that  sooner  or  later  injurious  concentrations  may 
even  result  from  tlie  use  of  only  slightly  saline  water.  The  more 
freely  the  water  penetrates  into  the  subsoil,  the  greater  will  be  the 
tendency  for  the  salts  to  be  leached  down  below  the  roots  of  plants, 
but  it  must  not  be  concluded  that  saline  water  can  be  applied  with 
imi)unity  to  a  porous  soil,  for  such  is  not  always  the  ca.se.  Even  here 
injurious  concentrations  may  accumulate.  As  will  be  shown  elsewhere, 
injur}'  may  be  produced  by  lesser  amounts  of  alkali  in  a  light  sandy 
soil  than  in  heavy  soil.  It  should  be  understood  that  sufficient  amounts 
of  water  to  leach  the  soil  effectively  are  rarely  applied  in  any  section 
of  California  and  especially  is  this  true  in  the  citrus  groves  where  the 
furrow  system  of  irrigation  is  used  and  the  supply  of  water  is  limited. 

THE    GROWTH    OF   CITRUS   TREES    ON    ALKALI    SOILS 

It  is  ([uitc  immaterial,  so  far  as  the  well-being  of  citrus  trees  is 
concerned,  or  of  other  erojis  for  that  matter,  whether  alkali  be  intro- 
duced into  the  soil  as  a  eonstitiu'nt  of  the  irrigation  water,  or  whether 


Bulletin  318       the  effects  of  alkali  ox  citrus  trees  319 

it  accumulate  there  as  a  result  of  other  afjencies.  The  net  effects  will 
be  similar,  provided  the  eoncentration  and  proportions  of  the  soluble 
constituents  in  contact  with  the  roots  be  the  same. 

Several  grov(  s  have  been  studied  where  alkali  salts  either  occurred 
originallj'  or  have  been  brought  up  recently  b}-  capillarity,  due  to  a 
high  water  table.  The  results  have  rev(ahd  some  information  addi- 
tional to  that  set  forth  above,  which  seems  to  be  of  sufficient  interest 
to  warrant  brief  discussion. 

A  twenty-year-old  lemon  grove  located  near  San  Diego,  that  has 
been  irrigated  with  reasonably  pure  water  the  greater  portion  of  the 
time,  has  been  studied.  During  the  past  few  years,  the  trees  have 
become  less  thrifty  than  formerly.  ]\Iany  of  the  older  leaves  have 
become  yellow  or  brown  in  irregularly  shaped  areas  around  their 
margins  and  have  fallen  excessively  at  certain  times.  Some  of  the 
leaves  are  variegated  and  show  the  usual  symptoms  of  mottle  leaf. 
The  yields  and  quality  of  the  fruit  have  also  depreciated. 

Soil  samples  to  a  depth  of  four  feet  have  been  analyzed,  and  the 
results  are  iTcorded  in  table  12.  The  data  show  that  this  soil  contains 
considerable  amounts  of  soluble  salts  of  which  sodium  is  the  predom- 
inant basic  constituent.  In  this  case,  however,  a  considerable  portion 
of  the  sodium,  especially  in  the  third  and  fourth  feet,  must  occur  in 
combination  other  than  the  chloride,  since  the  chlorine  content  is 
insufficient  to  combine  with  all  of  the  sodium  present.  The  data  indi- 
cate that  considerable  amounts  of  both  sodium  sulfate  and  sodium 
bicarbonate  occur  in  the  subsoil  layers.  The  water  table  is  many  feet 
below  the  surface  and  it  is  probable  that  a  large  portion  of  the  salts 
accumulated  in  the  subsoil  previous  to  modern  agriculture,  although 
the  irrigation  water  may  have  tended  to  increase  the  amounts  present. 

It  is  especially  interesting  that  the  roots  of  the  lemon  trees  have 
not  penetrated  deeply  in  tliis  soil,  more  than  95  per  cent  of  them 
being  within  eighteen  inches  of  the  surface.  There  is  probably  some 
connection  between  this  fact  and  the  higher  concentration  of  alkali 
salts  found  in  the  third  and  fourth  feet. 

The  above  discussion  should  not  be  interpreted  to  mean  that  a 
definite  degree  of  injury  to  a  given  variety  of  citrus  trees  can  always 
be  predicted  with  certainty  from  a  single  soil  analysis.  On  the  con- 
trary, other  faetoi-s  are  evidently  involved  in  tlie  problem  that  have 
not  yet  been  fully  evaluated.  The  following  discussion  is  of  interest 
in  this  connection. 

Local  areas  occur  in  a  A'alencia  orange  grove  near  Garden  (irove 
in  Orange  County  where  many  of  the  ti-ees  have  been  sevei'ely  injured 
by  aJJj/Tli  brought  up  as  a  result  of  a  tenipoi-arily  high  water  table  in 


320  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 

the  winter  and  sprin*;  of  1916.  The  water  table  receded  within  a  few 
months,  bnt  the  alkali  salts  remained  in  the  soil.  A  considerable  num- 
ber of  the  trees  have  recently  died,  and  all  of  them  in  certain  areas 
became  excessively  chlorotic,  following  the  rise  of  alkali. 

Soil  samples  have  been  drawn  from  an  area  where  the  orange  trees 
have  died  and  also  from  among  healthy  trees  near  b}^  the  analyses  of 
whieli  are  submitted  in  table  13.  The  results  show  that  a  high  con- 
centration of  a  inimber  of  salts  occurs  where  the  trees  have  died. 
The  amounts  of  chlorine,  sulfate,  sodium  and  calcium  are  all  excessive, 
extremely  so  in  the  case  of  sulfate.  The  concentration  is  undoubtedly 
])rohibitive  to  orange  tree  growth. 

On  the  other  hand,  the  concentration  of  soluble  sodium  in  the  soil 
where  the  trees  still  remain  healthy  is  ver}'  much  greater  than  was 
found  in  some  of  the  orange  groves  where  severe  injury  has  been  pro- 
duced by  saline  irrigation  waters.  In  this  case,  however,  the  sodium 
occurs  largely  as  sulfate  and  bicarbonate,  whereas  the  chloride  pre- 
dominated in  tlu^  former  case.  On  the  wliole,  the  results  obtained  in 
this  investigation  indicate  tliat  sodium  chloride  is  much  more  toxic 
to  citrus  trees  than  sodium  sulfate  or  sodium  bicarbonate,  which  is  in 
agreement  with  the  conclusions  of  Hilgard. 

An  eight-year-old  Navel  orange  grove  near  Bakersfield,  portions 
of  which  have  been  severely  injured  by  alkali,  has  also  been  studied. 
Analysis  of  soil  samples  (table  14)  reveals  a  very  high  concentration 
of  salts  where  the  trees  have  been  severely  injured.  With  the  excep- 
tion of  the  first  foot  of  this  soil,  the  concentration  of  chloride  is  not 
excessive,  but  sodium  sulfate  occurs  in  large  amounts.  Unusually  high 
nitrate  also  occurs  in  the  first  foot.  This  soil  is  also  supplied  with 
large  amounts  of  soluble  calcium,  the  nuiin  portion  of  which  occurs 
as  tlie  sulfate  (gypsum).  Extremely  large  amounts  of  gypsum  occur 
in  the  third,  fourth  and  fifth  feet. 

The  analysis  again  sliows  a  high  soluble  sodium  content  in  the  soil 
where  the  orange  trees  are  normal,  but  again  the  clilorine  is  low.  In 
the  first  three  feet,  the  sodium  is  largely  comb-ined  as  bicarbonate. 
In  the  second  and  third  feet,  considerable  amounts  of  the  normal 
carbonate  of  sodium  also  occur. 

It  will  be  noted  that  the  fourtli,  fifth  and  sixth  feet  of  this  soil 
contain  extremely  higli  concentrations  of  soluble  salts,  composed 
mainly  of  calcium  sulfate  and  sodium  sulfate.  The  roots  of  the 
healthy  trees  are  largely  confined  to  the  upper  two  feet  of  this  soil, 
and  so  long  as  they  remain  there  and  the  alkali  does  not  rise,  it  is 
possil)le  that  satisfactory  growtli  will  result.  It  is  highly  probable, 
however,  that  the  salts  will  tend  to  rise  as  a  result  of  capillarity  and 


Bulletin  318       tjj^  effects  of  alkali  on  citrus  trees  321 

every  precaution  should  be  taken  to  reduce  evaporation  to  the  lowest 
point  possible  and  thereby  retard  the  rise  of  salts. 

It  should  be  pointed  out  that  a  luimber  of  the  soils  studied,  where 
citrus  trees  have  been  severely  injured  by  alkali,  contain  abundant 
supplies  of  the  usual  plant  foods.  The  soluble  potassium,  nitrate  and 
phosphate  have  been  found  to  be  present  in  abundance  in  a  number 
of  those  soils.  It  is  highly  improbable,  therefore,  that  the  lack  of 
plant  food  has  contributed  to  the  unhealthy  condition  of  the  trees, 
or  that  the  use  of  commercial  fertilizers  will  effectively  overcome  the 
injury.  However,  it  should  be  stated  that  there  is  some  evidence  that 
an  abundant  supply  of  plant  food  does  enable  citrus  trees  to  overcome 
small  amounts  of  alkali.  On  the  other  hand,  it  is  reasonably  certain 
that  no  amount  of  ordinary  fertilizer  will  be  able  to  rejuvenate  the 
trees  where  large  amounts  of  alkali  occur. 

THE    EFFECTS    OF    SODIUM    NITRATE 

Investigations  at  the  Rothamsted  Station  in  England,  at  the  Penn- 
sylvania Station  in  this  country,  and  elsewhere,  have  been  interpreted 
to  mean  that  the  continued  application  of  sodium  nitrate  contributes 
to  the  formation  of  carbonates  in  soils.  The  presumption  has  been 
that  sodium  carbonate  is  formed  through  the  selective  absorption  of 
the  nitrate  (NO.,)  ion  by  the  crop  and  the  union  of  the  sodium  with 
the  ubiquitous  carbon  dioxide  of  soils.  We  are  not  awar£  that  this 
assumption  has  been  conclusively  proved,  the  published  evidence  being 
more  suggestive  than  conclusive. 

While  we  deem  it  to  be  highly  desirable  to  know  just  what  com- 
pounds actually  exist  in  a  given  soil,  and  recognize  that  dissimilar 
effects  are  likely  to  be  produc(>d  by  different  salts  of  the  same  base, 
it  is  nevertheless  true  that  any  salt  of  sodium  is  an  alkali  salt.  In  view 
of  the  possibility,  as  suggested  above,  that  sodium  nitrate  may  con- 
tribute to  the  formation  of  sodium  carbonate  (black  alkali)  in  soils, 
a  substance  commonly  regarded  as  injurious  to  plant  life,  and  that 
there  is  evidence  that  citrus  trees  may  be  abnormally  affected  by 
high  concentrations  of  sodium,  whatever  its  combination,  it  is  of  inter- 
est in  this  co7inection  to  study  the  effects  of  sodium  nitrate. 

Relatively  large  amounts  of  sodium  nitrate  have  been  applied  to 
citrus  groves  in  different  localities  in  California.  Tiie  fertilizer  plots 
of  the  Citrus  Experiment  Station  at  Riverside  afford  material  for  the 
study  of  tlie  effects.  One  of  these  ])lots  (H)  lias  l)een  fertilized 
exclusively  with  sodium  nitrate  for  the  past  twelve  years.  For  the 
past  six  years,  approximately  900  pounds  iiave  been  applied  per  acre 


322  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 

per  annum.  Prcvioush',  and  cspocially  durinj^  the  first  few  years  of 
the  experiment,  lesser  amounts  were  applied.  The  total  amount  that 
has  been  applied  as  an  aggregate  for  the  twelve  years  is  7944  pounds 
per  acre.  While  the  amounts  applied  have  undoubtedly  been  exces- 
sive during  the  past  five  years,  as  is  shown  by  the  soil  analysis,  the 
amounts  of  nitrogen  ajiplied  are  not  in  excess  of  that  sometimes 
applied  by  practical  citrus  growers,  who  occasionally  apply  as  much 
as  1000  pounds  of  sodium  nitrate  per  acre  during  a  single  season. 

The  control  plots  (B)  and  (I\I)  lie  adjacent  to  the  sodium  nitrate 
})lot.  Each  plot  contai)is  six  Navel  and  six  Valencia  orange  trees,  and 
six  Eureka  and  six  Lisbon  lemon  trees.  All  of  them  have  been  irrigated 
and  cidtivated  as  nearly  alike  as  passible.  During  the  first  five  or  six 
years  of  the  experiment,  the  growth  of  the  young  trees  of  each  variety 
was  markedly  stimulated  by  nitrate  of  soda.  The  soil  is  notably 
deficient  in  organic  matter  and  nitrogen  and  the  successful  culture  of 
non-leguminous  crops  requires  the  addition  of  considerable  nitrogen. 

While  the  growth  of  the  trees  was  notably  stimulated  by  sodium 
nitrate  during  the  first  few  3'ears  of  the  experiment,  and  healthy, 
normally  appearing  trees  were  produced,  since  that  time  excessive 
mottle  leaf  has  appeared  on  every  tree  in  this  plot.  The  mottling  here 
became  so  severe  during  the  past  two  or  three  years  as  to  render  the 
trees  wholh'  unprofitable.  No  marketable  fruit  whatever  is  now 
produced  by  these  trees. 

Soil  samples  from  the  control  and  sodium  nitrate  plots,  taken  to 
a  depth  of  six  feet  in  June,  1919,  show  the  effects  that  have  been 
produced  (table  15).  The  composition  of  the  soluble  matter  in  the 
soil  has  been  greatly  changed  as  a  result  of  applying  nitrate  of  soda. 
The  total  soluble  matter  has  been  increased  more  than  twofold  in  every 
foot  section  down  to  and  including  the  sixth  foot.  Among  the  indi- 
vidual constituents,  tlie  sodium  and  nitrate  have  been  most  markedly 
increased.  The  bicarbonate  has  also  been  increased  to  a  limited  extent, 
although  not  greatly,  but  the  soil  of  this  plot  has  not  accumulated 
any  soluble  normal  carbonate. 

This  soil  has  now  accumulated  a  considerable  amount  of  alkali 
merely  as  a  result  of  applying  sodium  nitrate  as  a  fertilizer  for  a 
period  of  twelve  years.  Its  suitability  for  the  growth  of  citrus  trees 
has  l)een  destroyed,  or  at  least  seriously  impaired.  The  alkali  in  this 
ease  is  largely  sodium  nitrate,  a  substance  of  unquestionable  value  as 
a  fertilizer  in  humid  climates  and  possibly  so  under  certain  soil  and 
climatic  conditions  in  the  semi-arid  west. 


Bulletin  318       the  EFFECTS  OF  ALKALI  ox  citrcs  trees  323 

THE    EFFECTS    OF    SALINE    IRRIGATION    WATER    AND    Na  NO,    ON    THE 
REACTION    OF   SOILS 

In  view  of  the  widespread  belief  tijat  sodium  carbonate  (l)laek 
alkali)  and  sodium  bicarbonate  are  the  most  toxic  constituents  that 
occur  in  alkali  soils  and  of  the  possibility  tiiat  the  injuiy  to  the  groves 
discussed  above  may  have  been  due  to,  or  at  least  associated  with, 
excessive  alkalinity  (Oll-ion  concentration),  the  reaction  of  a  con- 
siderable number  of  these  soils  has  been  determined  by  means  of  the 
hydrogen  glectrode. 

It  has  been  found  that  the  use  of  saline  irrigation  waters  Nos.  119, 
642  and  643,  ha.s  not  increased  the  alkalinity  of  the  soil  over  and  above 
that  occurring  where  good  irrigation  water  has  been  applied.  In  each 
case,  the  soil  is  distinctly  alkaline  in  the  chemical  sense  of  the  term, 
but  not  appreciably  more  so  where  the  saline  water  has  been  applied. 

In  the  comparisons  of  unirrigated  soil  with  soil  that  ha,s  been  irri- 
gated with  saline  water,  it  has  been  found  that  in  two  cases,  soils  T 
and  Y,  there  appears  to  have  been  an  appreciable  increase  in  alkalinity 
as  a  result  of  irrigation,  while  in  the  case  of  soil  II,  there  has  been 
a  decrease. 

In  order  to  study  the  effects  of  sodium  nitrate  on  soil  alkalinity, 
tests  have  been  made  on  each  of  the  control  plots  (B  and  M)  that  lie 
adjacent  to  the  sodium  nitrate  plot  (II) .  The  results  leave  some  doubt 
whether  the  reaction  has  been  materially  changed  as  a  result  of  apply- 
ing sodium  nitrate.  It  should  be  pointed  out,  however,  that  the  soil 
of  each  of  these  plots  is  distinctly  alkaline  and  it  does  not  follow  from 
these  results  that  the  application  of  sodium  nitrate  to  an  acid  soil 
might  not  tend  to  lower  the  acidity. 

A  determination  of  the  reaction  of  other  soils  not  reported  herein 
has  shown  equally  as  high  a  degree  of  alkalinity  (OH-ion)  where 
healthy  citrus  trees  are  being  grown,  as  in  the  severely  injured  groves. 
We  are  inclined  to  conclude,  therefore,  that  excessive  alkalinity  is  not 
the  cause  of  the  injury,  either  in  the  ease  of  saline  irrigation  waters. 
or  where  sodium  nitrate  has  been  applied  as  a  fertilizer.  Excessive 
concentration  of  sodium  as  such,  together  witli  tlie  relationships  it 
bears  to  the  concentration  of  other  constituents  ])resent,  is  prol)al)ly 
more  fundamentally  responsible  for  the  injury. 

DISCUSSION 

The  results  of  recent  investigations  establish  tlie  fact  that  some  of 
the  irrigation  waters  in  use  at  the  jiresent  tinu>  on  the  eitiiis  groves  of 
California  are  higlily  charged  with  alkali;  otiiers  contain  soniewliat 

DIVI540N  OF  sijfsr.vnri::AL  horiiculiuke 

COLLEGE  OF  AGRICULTURE 


324  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 

lesser  amounts,  while  a  much  larger  proportion  contains  intermediate 
quantities  of  salts.  Fortunately,  however,  a  very  large  proportion 
of  the  irrigation  water  is  highly  satisfactory  in  quality. 

It  has  been  found  that  a  considerale  number  of  citrus  groves 
located  in  several  districts  in  California  have  already  been  severely 
injured  by  alkali  and  that  a  large  percentage  of  the  injury  is  due  to 
the  irrigation  water. 

The  comments  of  Hilgard  made  in  1900  relative  to  the  use  of  saline 
irrigation  water  may  be  appropriately  quoted  at  this  time :" 

Means  and  Gardner"  have  called  attention  to  the  fact  that  exces- 
sively saline  irrigation  waters  have  been  applied  to  the  soils  of  certain 
portions  of  the  Pecos  Valley,  New  Mexico,  and  that  severe  damage  has 
been  produced  as  a  result.  In  discussing  this  problem  in  1899,  they 
said :  "The  soils  were  shown  to  contain  originally  only  small  quantities 
of  alkali  salts  in  their  natural  state,  but  at  present  there  are  areas 
containing  great  quantities  of  such  salts.  The  presence  of  this  alkali 
ma}',  in  nearly  all  cases,  be  attributed  mainly  to  the  salt  which  is 
contained  in  the  irrigation  water.  .  .  .  The  character  of  the  water  is 
the  most  serious  difficulty  in  the  way  of  profitable  irrigation.  To 
develop  a  new  supply  of  water  would  be  an  engineering  problem 
difficult  of  solution.  The  use  of  the  present  supply  is  attended  with 
possible  loss  of  crops,  especially  where  the  most  favorable  conditions 
do  not  exist." 

Forbes'*  showed  that  the  irrigation  waters  of  the  Salt  River  and 
other  valleys  of  Arizona  are  supplying  large  amounts  of  salts  to  the 
soils.  From  soil  analj'sis  he  found  that  the  salt  content  of  the  soil 
had  been  materially  increased  in  consequence  of  applying  saline 
water. 


G  Calif.  Agr.  Exp.  Sta.  Bull.  128  (1900),  p.  30. 

It  would  hardly  seem  necessary  to  emphasize  specially,  the  danger  incurred  in 
irrigation  with  waters  containing  unusual  amounts  of  soluble  salts;  since  ordinary 
common  sense  clearly  indicates  the  impropriety  of  increasing  the  saline  contents 
of  soils  already  charged  with  them,  by  the  evaporation,  year  after  year,  of  large 
masses  of  saline  wat«r.  Yet  experience  has  shown  that  the  eagerness  to  utilize 
for  irrigation  whatever  Avater  happens  to  be  convenient  to  good  lands,  often  over- 
comes both  that  sense,  and  Avarning,  given  ])y  the  published  analyses  of  such 
waters.  Without  specifying  localities,  it  may  be  said  that  great  injury  has  already 
been  done  in  California  by  the  disregard  of  obviously  needful  caution  in  this 
respect.  The  very  slight  taste  possessed  by  glauber  salt  and  salsoda  does  not 
adequately  indicate  their  presence,  even  when  in  injurious  amounts;  so  that  fre- 
quently a  chemical  test  of  the  waters  is  the  only  definite  guide. 

"  A  Soil  Rurvev  of  the  Pecos  Vallev,  New  Mexico.  U.  S.  Dept.  Agr.,  Report  64, 
pp.  :5(>-7(5. 

■^  The  Kiver  Irrigating  Waters  of  Arizona — Their  Cliaracter  and  Effects.  Ariz. 
Agr.  Exp.  Sta.  Bull.  44,  1902. 


Bulletin  318       the  EFFECTS  OF  alkali  ox   citrus  trees  325 

Chlorides  are  undoubtedly  the  most  injurious  constituents  that 
occur  in  the  irrigation  waters  of  southern  California,  but  it  must  not 
be  concluded  that  other  alkali  salts  can  be  ignored.  In  certain  locali- 
ties some  of  the  waters  also  contain  injurious  amounts  of  sulfates  and 
carbonates.  Ililgard  says,  "Unfortunately  it  is  not  easy  to  give  abso- 
lute rules  in  regard  to  the  exact  figures  that  constitute  an  excess  of 
salts  for  irrigation  purpose  s,  since  not  only  the  composition  of  the  salts, 
but  the  nature  of  the  land  to  be  irrigated,  and  the  frequency  of  irriga- 
tion required,  must  be  taken  into  consideration."  He  concluded  that 
40  grains  per  gallon  (684  parts  per  million)  is  the  maximum  amount 
of  the  total  mineral  matter  a  water  can  safely  contain,  unless  the 
mineral  constituents  be  composed  largely  of  gypsum.  But  he  also 
said:  "When  a  large  proportion  of  the  solids  consists  of  carbonate  of 
soda  or  common  salt,  even  a  snialhr  proportion  of  salts  tJuin  40  grains 
might  preclude  its  regular  use."  We  regret  to  state  that  a  consider- 
able number  of  irrigation  waters  contain  salts  in  excess  of  this  limit, 
some  of  them  greatly  so. 

It  has  also  been  shown  that  tlie  continued  application  of  nitrate 
of  soda  may  bring  about  an  increase  in  the  amounts  of  alkali  in  the 
soil.  It  is  true,  the  amount  of  nitrate  that  has  been  applied  to  the 
experimental  plot  we  have  studied  is  excessive  and  the  results  might 
have  been  different  on  other  soil  or  even  on  the  same  soil,  had  it  been 
treated  differently  in  other  respects.  If  nitrate  of  soda  be  applied 
in  moderate  quantities  to  a  porous  soil,  especially  where  the  rainfall 
is  heavy,  or  if  used  in  conjunction  with  manure  and  cover  crops,  it 
is  highly  probable  that  the  sodiinn  will  be  leached  more  deeply  than 
it  has  been  on  the  experimental  plot  at  Riverside. 

However,  it  is  especially  important  for  farmers  to  understand 
clearly  that  citrus  treses,  as  well  as  many  other  crops,  do  not  absorb 
more  than  ver}'  limited  amounts  of  sodium,  and  that  wherever  nitrate 
of  soda  be  applied,  eitlier  in  combination  with  other  fertilizer  con- 
stituents or  alone,  the  sodium  will,  for  the  most  part,  be  rejected  b}-  the 
crop  and  left  in  the  soil.  This  sodium  remains  mostly  in  soluble  form 
and  contributes  directly  to  the  alkali  conteiit  of  the  soil. 

All  sodium  salts  are  really  alkali  salts.  As  has  been  repeatedly 
stated,  small  amounts  of  none  of  them  arc  injurious,  and  in  the  case 
of  the  nitrate,  limited  amounts  undoubtedly  stimulate  the  growth  of 
practically  all  crops;  but  unless  drainage'  ett'ectively  leach  the  salts 
from  the  soil,  the  continued  application  of  sodium  nitrate,  or  of  saline 
irrigation  water,  will  ultimately  produei'  a  hainiful  eoneentration  of 
alkali  in  any  soil. 


326  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 

It  is  also  a  matter  of  practical  importance,  that  the  repeated  appli- 
cation of  any  sodium  salt  to  soils,  followed  by  leaching  with  irrigation 
w^ater,  or  rains,  tends  to  reduce  the  porosity  of  the  soil  and  thereby 
restricts  the  movement  of  the  water  through  it.  Sodium  carbonate 
and  sodium  bicarbonate  probably  produce  this  effect  to  a  greater 
extent  tiian  tiie  other  common  sodium  salts,  but  all  of  them  produce 
til  is  eft'ect  to  an  undesirable  extent.  The  experimental  plot  to  which 
nitrate  of  soda  has  been  applied,  has  become  badly  puddled,  and  the 
poor  physical  condition  of  the  subsoil  in  a  number  of  the  groves  where 
saline  watere  have  been  applied,  form  one  of  their  striking  character- 
istics. The  surface  soil  in  some  of  these  groves  has  become  exceedingly 
baked,  so  much  so  as  to  be  readily  detectable  by  merely  walking  over 
it.  Hence,  the  effects  of  alkali  are  not  wholly  determined  by  the  con- 
centration of  salts  in  the  soil.  The  adverse  physical  conditions  must 
also  be  considered. 

Therefore,  wherever  nitrate  of  soda  or  saline  irrigation  water 
be  used  in  regions  of  light  rainfall,  especially  if  applied  for  any  con- 
siderable length  of  time,  it  is  important  for  farmers  to  understand 
that  the  soil  must  be  kept  open  and  porous.  Tliis  can  probably  best 
be  accomplished  by  growing  deep-rooted  cover  crops  and  plowing 
under  organic  materials,  such  as  manure  or  bean  straw. 

While  ordinary  irrigation  and  rains  tend  to  leach  more  or  less 
alkali  down  below  the  reach  of  citrus  roots  and  probably  accomplish 
this  end  quite  effectively  in  some  soils,  our  investigations  show  that 
the  application  of  saline  water  has  resulted  in  materially'  increasing 
the  amounts  of  alkali  witliin  reach  of  the  roots  of  the  citrus  trees.  The 
soil  types  and  climatic  conditions  of  these  groves  vary  widel}'.  Some 
of  them,  not  reported  above,  occur  in  the  districts  of  comparatively 
heavy  rainfall  and  on  soils  ordinarily  considered  to  be  naturally  well 
drained. 

As  suggested  above,  the  irrigation  supjilies  rarely  contain  enough 
alkali  to  harm  citrus  trees  directly.  So  far  as  we  have  been  able  to 
learn,  no  detrimental  effects  occurred  in  any  of  the  groves  until  after 
the  saline  waters  had  been  apjilied  for  a  period  of  years.  The  injury 
came  about  rather  through  the  concentration  resulting  from  the 
accumulated  residue,  left  by  the  evaporation  of  repeated  applications 
of  watei',  as  was  pointed  out  by  Dr.  llilgard  many  years  ago. 

An  excess  of  chlorides  causes  the  tips  and  margins  of  citrus  leaves 
to  l)eeome  yellow  or  brown,  followed  b}-  defoliation.  Sometimes  a  large 
portion  of  the  haves  fall  and  the  young,  tendi'r  slioots  may  be  killed. 
An  excess  of  sulfates  and  biearbonates,  on  the  other  hand,  is  more 
likelv  to  stunt  the  growth  of  the  trees  and  cause  the  leaves  to  become 


Bulletin   318         ^jik    EFFECTS    OF    ALKALI    ON    OITRCS    TREES  327 

chlorotic.  More  or  less  mottle  leaf  may  also  occur.  Lemon  trees  are 
apparently  injured  by  lesser  amounts  of  alkali  tiian  oranj^cs. 

On  the  whole,  the  observations  and  conclusions  of  Ililj^ard  and 
Loughridge  have  been  strikingly  confirmed.  It  ha.s  again  been  shown 
that  citrus  trees  are  quite  sensitive  to  alkali  and  especially  to  sodium 
chloride.  It  is  a  matter  of  practical  importance  for  citrus  growers 
to  recogni/.e  this  fact,  for  sodium  chloride  is  the  one  constituent  most 
commonly  found  in  irrigation  waters  that  are  drawn  from  wells  in 
the  citrus  sections  of  California. 

As  for  the  treatment  of  the  injured  groves,  nothing  more  than  the 
most  general  suggestion  can  be  offered  at  present.  AVhere  saline  irri- 
gation water  is  being  apjilied.  the  first  consideration  sliould  be  to 
secure  an  adecpuite  supply  of  i)ure  water.  In  fact,  so  long  as  the 
application  of  saline  water  be  continued,  it  will  be  difficult  to  over- 
come the  harmful  etTects  by  any  method  that  may  be  devised. 

As  suggested  by  Forbes-^  an  occasional  flooding  may  improve  the 
conditions,  by  leaching  the  salts  below  the  reach  of  the  roots,  but 
before  flooding  be  undertaken,  tlie  irrigator  should  assure  himself 
that  the  subsoil  is  of  such  character  as  will  permit  deep  penetration 
of  the  water  and  allow  it  to  drain  away.  Otherwise,  his  eft'orts  will 
be  wasted.  x\fter  the  salts  have  been  washed  down  below,  the  soil 
should  be  thoroughly  cultivated  in  order  to  reduce  evaporation  and 
thereby  check  the  rise  of  salts. 

Where  saline  water  is  the  only  irrigation  supply  that  can  possibly 
be  obtained,  it  may  be  found  desirable,  in  some  cases  at  lea.st,  to  dis- 
continue the  furrow  system  of  irrigation  entirely  and  adopt  some  form 
of  basin  or  flooding  irrigation  instead.  By  that  means,  the  tendency 
will  be  to  leach  the  salts  down  into  the  subsoil  and  possibly  below  the 
reach  of  citrus  roots.  The  success  of  such  a  scheme  will  depend  largely 
on  the  natui'e  of  the  subsoil  drainage  and  the  thoroughness  with  which 
it  is  executed.  In  addition,  the  leaching  effects  of  the  winter  rains 
sliould  be  taken  advantage  of  to  the  greatest  extent  possible.  As  a 
means  to  this  end,  the  soil  should  be  put  into  such  condition  previous 
to  the  I'ainy  season,  as  will  prevent  surface  run-oft'  and  enabl(>  the 
rain  water  to  peneti'ate  deeply. 

It  sliould  be  borne  in  mind,  however,  that  alkali  sails  are  being 
di'iven  down  into  the  subsoil  and  that  there  is  a  constant  danger  of 
the  salts  rising  up  around  the  roots.  Furthermore,  the  contimied 
addition  of  such  large  amounts  of  salts  as  occur  in  some  of  the  irriga- 
tion  waters,   will   materiallv   inerease  the  salt   content   of  the   natural 


•-'Ariz.  A>,n-.  Exp.  Stii.  T?ull.  44   (l!t02\  ].i>.   Kw    170. 


328  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 

drainage  water.  In  localities  where  the  volume  of  the  drainage  water 
resulting  from  such  leaching  constitutes  any  considerable  portion  of 
the  natural  drainage  water,  the  ground  water  may  ultimately  become 
heavih'  charged  with  salts  as  a  result.  This  is  especially  to  be  feared 
where  the  ground  water  is  rising  or  is  already  near  the  surface.  In 
view  of  these  facts,  the  application  of  saline  irrigation  water  should 
be  avoided,  whenever  possible. 

The  experience  of  the  growers  near  (^orona,  following  the  use  of 
water  fnmi  Lake  Elsinore,  is  of  sjiecial  interest  at  this  time.  Some 
of  the  groves  that  were  severely  injured  then,  have  since  recovered 
and  have  borne  profitable  crops  of  fruit,  while  others  have  not  yet 
fully  recovered.  In  general,  the  most  effective  treatment  was  found 
to  consist  of  thorough  tillage,  plowing  down  manure  and  the  applica- 
tion of  suitable  irrigation  water. 

If  good  water  be  applied  freely  it  is  probable  that  the  harmful 
concentrations  of  salts  that  have  accumulated  will  be  gradually  leached 
down  below  the  reach  of  the  roots  and  the  use  of  manure,  coupled  with 
deep  plowing,  will  gradually  restore  conditions  favorable  to  growth. 
As  a  means  of  further  increasing  the  porosity  of  the  soil,  an  applica- 
tion of  gypsum  may  also  be  desirable.  In  addition  to  its  flocculating 
effect,  gypsum,  and  other  calcium  salts  also,  seem  to  ameliorate  the 
effects  of  toxic  concentrations  of  alkali  salts,  and  enable  crops  to 
tolerate  concentrations  of  alkali  salts  that  are  prohibitive  of  normal 
growth  in  the  absence  of  an  abundance  of  calcium  salts. 

AVhile  somewhat  apart  from  this  investigation,  it  may  be  appro- 
priate to  state,  that  a  limited  study  of  the  amounts  of  water  available 
to  the  citrus  groves  of  California  leads  us  to  believe  that  the  most 
promising  source  from  which  a  supply  of  really  good  water  can  be 
secured  in  quantities  sufficient  to  meet  the  demands  of  the  constantly 
expanding  citrus  industry,  can  be  obtained  only  througli  concerted 
effort  directed  towards  the  control  of  flood  waters.  By  the  use  of 
suitable  check  dams,  reservoirs,  reforestation,  and  such  otiier  devices 
as  will  permit  the  storage  of  tiie  mountain  waters,  either  above  ground 
or  within  the  water-bearing  gravels,  an  adequate  supply  of  suitable 
water  can  probably  be  obtained.  At  any  rate,  the  excellent  water 
that  falls  in  the  mountains  of  California,  may  be  so  conserved  as 
to  augment  materially  the  volume  of  water  now  being  obtained  from 
them,  and  thereby  make  it  possible  to  discontiiuie  the  use  of  at  least 
a  portion  of  the  saline  water.^° 


1"  A(kii()\\i('(l<,niu'nt    is    due    Mr.    A.    R.    Cuiiiiiiins    and    Mr.    8.    M.    Brown    for 
annlvticTil  assistance  rendcri'd  i7i  connection  \vith  this  investi<;ation. 


Bulletin   318         the    EFFECTS    OF    ALKALI    ON    CITRl'S    TREES 


329 


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Bulletin  318        'pjj^    kffects   OF   ALKALI   ON    CITKI'S   TREKS  331 


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332 


UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 


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